The Location of Multifidus Atrophy in Patients With a Single Level, Unilateral Lumbar Radiculopathy

OBJECTIVE To identify the correlations between the location of multifidus atrophy and the level of lumbar radiculopathy. METHODS Thirty-seven patients who had unilateral L4 or L5 radiculopathy were divided into 2 groups; the L4 radiculopathy (L4 RAD) group and the L5 radiculopathy (L5 RAD) group. Bilateral lumbar multifidus muscles at the mid-spinous process level of L4 vertebra (L4 MSP), the mid-spinous process level of L5 vertebra (L5 MSP), and the mid-sacral crest level of S1 vertebra (S1 MSC) were detected in T1 axial magnetic resonance imaging. The total muscle cross-sectional area of multifidus muscles (TMCSA) and the pure muscle cross-sectional area of multifidus muscles (PMCSA) were measured by a computerized analysis program, and the ratio of PMCSA to TMCSA (PMCSA/TMCSA) was calculated. RESULTS There were no significant differences in TMCSA between the involved and the uninvolved sides in both groups. PMCSA was only significantly smaller at the S1 MSC on the involved side as compared with the uninvolved side in the L5 RAD group. The ratio of PMCSA to TMCSA was the lowest at the L5 MSP on the involved side in the L4 RAD group and at the S1 MSC on the involved side in the L5 RAD group. CONCLUSION Our findings suggest that the most severe atrophy of multifidus muscle may occur at the mid-spinous process or mid-sacral crest level of the vertebra which is one level below the segmental number of the involved nerve root in patients with a single-level, unilateral lumbar radiculopathy.